1. Field of the Invention
This invention generally relates to a data receiver, and specifically relates to a radio receiver for frequency shift keyed (FSK) signals representing data.
2. Description of the Prior Art
In some cases, data transmission is made via radio communication equipments which use data-representing FSK signals on a radio frequency (RF) carrier.
U.S. Pat. No. 4,462,107 corresponding to Japanese published unexamined patent application 58-19038 discloses a direct-conversion radio receiver for FSK signals which includes a pair of signal paths having respective mixers. Quadrature outputs of these mixers are low-pass filtered, and a 90-degree phase shift at a base band frequency is introduced in one signal path. The base band signals are then fully limited and applied to a logic network to provide a digital output indicative of the relative lead/lag condition of the two signal paths.
In the radio receiver of U.S. Pat. No. 4,462,107, the digital output tends to be contaminated by errors at considerable rates as the frequency of a local oscillator signal deviates from the frequency of the RF carrier.